Details of such composite formulations are recited in the following citations:
U.S. Pat. No. 2,528,235, to J. A. Loritsch, patented Oct. 31, 1950, note in particular Example 13 of the patent;
U.S. Pat. No. 3,261,886, to J. R. Lowry, patented July 19, 1966;
U.S. Pat. No. 2,757,160, to T. A. Anderson, patented July 31, 1956;
British patent specification No. 937,703, to DEGUSSA, published Sept. 25, 1963;
U.S. Pat. No. 3,701,748, to C. H. Kroekel, patented Oct. 31, 1972;
U.S. Pat. No. 3,549,586, to P. L. Smith and L. R. Comstock, patented Dec. 22, 1970;
U.S. Pat. No. 3,668,178, to L. R. Comstock and P. L. Smith, patented June 6, 1972;
U.S. Pat. No. 3,718,714, to L. R. Comstock and P. L. Smith, patented Feb. 27, 1973.
Other reference citations of interest include:
U.S. Pat. Nos. 3,642,672; 3,772,241, 3,711,432; 3,503,921; 3,551,378, 3,721,642; 3,736,728; 3,489,707; and 3,642,683;
German Applications Nos. 2,305,246 (9/6/73); 2,252,972 (5/24/73); 2,225,736 (1/18/73); 2,223,463 (11/23/72); 2,139,330 (2/15/73); 2,163,089 (6/20/73); and 2,064,148 (12/28/70);
Japanese Patent Nos. 4,847,543 (7/6/73); 4,851,090 (7/18/73); 4,849,884 (7/13/73); 73-00197 (1/6/73); 73-21,788 (3/19/73); 73-20,887 (3/15/73); 4,861,592 (8/29/73); 73-21,787 (3/19/73); 73-08873 (3/17/73); 73-21,784 (3/19/73); and 4,601,789 (10/1/71);
Netherlands Applications Nos. 72-03034 (9/12/72); 72-156147 (5/22/73); 72-08269 (12/19/72); 70-15386 (4/26/71); and 70-14568 (6/17/71);
British Patent Specifications Nos. 1,321,686 (6/27/73); and 936,351 (9/11/63);
Belgium Patent No. 740,581; and
Canadian Patent No. 887,693.
Illustrative of texts dealing with polyester resins and composites made from them are the following:
Bjorksten Research Laboratories, "Polyester and Their Applications", Reinhold Publishing Corp., New York, 1956.
Herman V. Boenig, "Unsaturated Polyesters: Structure and Properties", Elsevier Publishing Company, Amsterdam, 1964.
W. S. Penn, "GRP Technology", Maclaren & Sons, Ltd., London, 1966.
E. N. Doyle, "The Development and Use of Polyester Products", McGraw-Hill Book Co., New York, 1969.
Of particular significance to this invention are the following background references which deal with the use of alumina trihydrate in such polyester resin composites or the treatment of alumina trihydrate fillers with silane adhesion promoters.
(1) U.S. Pat. No. 2,768,264, patented Oct. 23, 1956, describes the use of alumina trihydrate ("hydrated alumina") in polyester resin composition to improve electrical properties, specifically arc suppression. In this regard, reference is made to U.S. Pat. Nos. 2,997,526-8.
(2) Ampthor and Kroekel, in the paper titled "Developments in Low-Profile SMC For Flame Retardant and Electrical Applications", published in Section 8-E of the preprints of the 27th Annual Technical Conference, 1972 Reinforced Plastics/Composites Institute of The Society of the Plastics Industry, Inc., New York, New York, cite the use of alumina trihydrate in polyester resin systems which contain acrylate thermoplastic low profile additives for the purpose of enhancing flame retardancy and electrical properties.
(3) W. J. Connolly and A. M. Thorton, in an article entitled "Aluminum Hydrate Filler in Polyester Systems", Modern Plastics, 43 (2), 154, 156, 202 (1965) report that: "Aluminum hydrate used at appropriate loading in polyester premix and laminating systems imparts excellent flame retardancy, heat stability, and hydrolysis resistance to the plastic. This system has an economic advantage over the conventional halogen-antimony trioxide flame resistance system".
(4) U.S. Pat. No. 3,189,513, to Calderwood et al., describes the addition of alumina trihydrate to a specific chlorinated polyester to produce a product which can be favorably employed in electrical application.
(5) U.S. Pat. No. 3,647,742, to John Stevens, shows that the addition of a small amount of a cycloaliphatic epoxy substituted silane such as one having the formula: ##STR1## to the surface of alumina trihydrate enhanced the tensile strength and elongation of a cycloaliphatic epoxide composite into which it is incorporated. This represented the first indication that a silane adhesion promoter, albeit a most specific one, could be used to enhance the reinforcing properties of aluminum trihydrate.
(6) Dzik, McNally and Williams, in a paper entitled "Low Shrinkage Plus Flame Retardance", presented at the aforementioned 27th Annual Technical Conference [see item (2) above], stated that Kopper Company, Inc., Pittsburgh, Pennsylvania, had developed a "complex" low shrink self-extinguishing polyester formulation which utilizes a proprietary resin mixture of two incompatible halogenated resins (as styrene solutions), alumina trihydrate and antimony trioxide.
(7) Byrd, in an article entitled "Flame Retardant Polyesters -- Two Approaches", Section 23-D, (February 1974) of the preprints of the 29th Annual Conference, Reinforced Plastics/Composite Institute, The Society of the Plastic Industry, Inc. (250 Park Avenue, New York, New York 10017), discusses a variety of complex resin systems some of which utilize alumina trihydrate to control flame retardancy, generally in combination with other known flame retardants.
(8) Waycheshin and Sobolev, in their article entitled "Effect Of Particle Size On The Performance Of Alumina Hydrate In Glass-Reinforced Polyesters", 30th Anniversary Conference, February 1975, Reinforced Plastics/Composites Institute, The Society of the Plastics Industry, Inc., supra., state that particle size of alumina trihydrate has little influence on the physical properties and only a slight effect on the flammability of glass-reinforced polyesters.
(9) Ranney, Berger, and Marsden, in an article entitled "Silane Coupling Agents In Particulate Mineral-Filled Composites", Section 21-D, preprints of the 27th Annual Technical Conference, supra., item (2) above, discuss the use by integral blending techniques of A-174 (gammamethacryloxypropyltrimethoxysilane) with hydrated alumina in a polyester resin formulation to provide the typically expected improvement in wet strength property retention (Table VII) and, in addition, a suggestion of improvement as well in dry flexural strength (Table IX). No glass fiber is shown in these specific disclosures of hydrated alumina. It should be noted that Ranney et al. repeat the information of Stevens (item 5 above) on the treatment of hydrated alumina with an epoxy silane adhesion promoter.
At the outset, the terms "adhesion promoter(s)" and "coupling agent(s)" are intended when refering to organofunctional silanes to have the same meaning and should be recognized as synonyms in this art. The terms will be interchanged for that reason.
In summarizing the prior art, these statements seem relevant:
(a) The methods of making glass fiber reinforced plastics ("GRP") and, in particular, glass fiber reinforced thermosetting polyesters is a well developed art.
(b) That in producing any GRP, the strength of the composite is derived from the glass fiber content.
(c) That in efforts to improve the flame retardance of such products, the art has employed chlorinated or brominated polyester resins, alone or in combination with other known flame retardants such as antimony trioxide, phosphorus compounds and/or alumina trihydrate.
(d) That efforts to obtain favorable flame retardancy in a GRP based essentially on a conventional polyester and alumina trihydrate indicate critical problems in handling the loaded resin paste formed from the resin, the fiber content and the alumina trihydrate. The viscosity build-up derived from the inclusion of alumina trihydrate complicates the ability to achieve a system containing enough of the hydrate to give meaningful flame retardancy (see Item 2 above). The problem of filler loadings in GRP's is mentioned by W. S. Penn, supra., at pages 141-145.
(e) That silane adhesion promoters can be used in non GRP systems to enhance the flexural strength, both wet or dry, of alumina trihydrate in an unsaturated polyester resin.
(f) That high filler loadings of GRP can adversely affect the strength properties of the resulting composite, see, e.g., page 94 of the Bjorksten Research Laboratories text, supra., and W. S. Penn, supra., as noted in item (d) above.
One can conclude from the prior art that the following constitutes critical objectives for a flame retardant GRP based on thermosetting polyester resins:
A. Such a GRP should not be dependent upon expensive chlorinated and/or brominated polyester resins.
B. Antimony trioxide should be removed from such a GRP (or its content should be minimized) owing to its fluctuating availability and cost, and its deleterious effects on physical properties such as tensile and flexural strengths.
C. The GRP system must have workable viscosities in the mixing and compounding equipment and good flow in the mold.
D. One should achieve at least the physical properties of traditional GRP which the flame retardant GRP is designed to replace.